Plasmonic membranes as novel bio-detection substrates for surface-enhanced raman spectroscopy

A novel substrate based on hydrophobic membranes decorated with a 2D-assembly of silver nanowires (AgNWs) is presented. Here we are aimed at implementing a SERS biosensor obtained by simple and cost-effective fabrication procedures, ensuring a highly sensitive, reproducible and uniform SERS signal from biomolecules in trace amounts [1,2]. The choice of high-aspect-ratio silver nanostructures is justified by the advantage of their facile synthesis and exceptional capability of self organizing into complex 2D assemblies with high degree of hot spot formation and improved electromagnetic enhancement of the Raman scattering [3]. A low-density clustered layer of AgNWs was achieved either by filtration through a porous Teflon membrane or by ink-jet printing on the surface of the membrane. The resulting high contact angle of a drop of aqueous solution on top of the AgNWs-decorated membrane upon evaporation allows the molecules to concentrate into small spots on the surface. Thereby a large number of molecules can get in close proximity to the hot spot regions of the plasmonic nanowires yielding an enhancement factor of the Raman intensity of the species of about 10^5. The novel AgNWs-decorated membranes were efficiently tested as a SERS bio-detection platform on proteins, oligonucleotides and amyloid oligomers. Thus, thanks to a simple and low-cost fabrication procedure, a high sensitivity and reproducibility as well as an overall performance improvement due to analyte concentration on the SERS hot spots, the proposed substrates can be used as effective tools for SERS analysis of molecules of biomedical interest.